Orthopedic injuries, deformities, and degenerative diseases often require intervention in the form of surgery for placing implants to stabilize an internal structure, promote healing, and relieve pain. In the area of spinal surgery, for example, a common procedure includes placement of pedicle screws that are joined by a connecting rod spanning between these screws. Once placed, the rod must be firmly secured to the bone securing elements to provide a stable construct which effectively immobilizes or creates a controlled dynamic motion to a corresponding portion of the spine.
One problem when connecting the rods to the pedicle screws is to position the rods in place as quickly as possible without doing more damage to the surrounding tissue and muscle of the patient. In order to reduce this damage, procedures have been developed that allow the physician to secure the pedicle screws in the bony portion of the spine and to then connect the rods or brace between the pedicle screws. Techniques have been developed to allow the surgeon to perform this procedure in a minimally invasive manner, utilizing a percutaneous method, inserting screws through small ports and avoiding an open approach.
In one such procedure, a surgeon identifies the desired vertebral level and pedicle positions via standard techniques. Once the target vertebrae are identified, a small incision is made through the patient's skin and a tracking needle (or other device) is inserted to pinpoint exactly where each pedicle screw is to be placed. A fluoroscope, or other x-ray technique, is used to properly position the tracking needle. Once the proper position is located, a guide wire is positioned with its distal end into the pedicle of vertebrae. The surgeon then slides a series of continuing larger sized dilators down the guide wire. The surgeon may also slide a hole tapping instrument over the guide wires. The hole tapping instrument may be used to tap a hole in the pedicle. After the hole is tapped, a cannulated pedicle screw and a modified screw driver may be inserted down the guide wire until the screw reaches the desired position. The position may be again checked with fluoroscopic techniques. For purposes of this application, a cannulated pedicle screw is defined as a pedicle screw that contains a cannulation centered and running entirely through its longitudinal axis.
After the position of the cannulated pedicle screw has been confirmed, the surgeon is ready to screw the cannulated pedicle screw into the vertebrae. After the cannulated pedicle screw has been inserted, this procedure may be repeated for each additional level. When one or more pedicle screws are in place, a brace or rod may be positioned by techniques known in the art. Under current practice, the physician then must work the brace, or other supporting device, so that each brace end is positioned properly with respect to the preplaced pedicle screws, and tighten the brace to each pedicle screw to complete assembly.
Once a patient recovers and become active, the brace may be subject to relatively large structural forces. These forces are applied to the shanks of the cannulated pedicle screws. Consequently, it is the shanks of the cannulated pedicle screws that resist the applied forces. To be more specific, it is the portion of the screw shank that is positioned within the pedicle of the vertebral body (approximately two-thirds of the length of the screw from the distal tip of the screw towards the proximal end of the screw) (the highest stress region is that region of the pedicle screw that is nearest the entry point of the pedicle, which tends to be about two thirds up from the distal tip of the pedicle screw).
When conventional pedicle screws are cannulated, a significant portion of their cross-sectional area is removed to create the cannulation. The cannulation, therefore, causes higher stress in the remaining portions of the shank which is subject to the applied forces. This causes a significant weakening of the screw. This weakening can cause failure of the pedicle screw which means that the patient would have to undergo additional surgery to have the pedicle screws replaced.
In order to minimize the reduction in strength of the screws, the cannulations are made as small as possible. This means that the guides wires must also be small, which may lead to advancement, kinking, breakage, or other problems during surgery. Inadvertent advancement of the guide wire is a critical concern to clinicians. If the guide wire becomes bent through off-angle manipulation by the surgeon, as the tap or screw is inserted, the tap or screw pushes the guide wire forward. This unwanted guide wire advancement could cause the guide wire to push forward through the anterior wall of the vertebral body, causing trauma to the patient.
What is needed, therefore, is a device and system which will allow for anchors to be guided and inserted into patients while maintaining the structural integrity and safety of the anchor and/or the guide wire.